For a child weighing 16.78 kg with no drug allergies, how should I prescribe amoxicillin suspension 400 mg/5 mL (80 mg/mL) – dose, frequency, duration, and quantity?

Amoxicillin Prescription for a 16.78 kg Child

For this 16.78 kg child with no drug allergies, prescribe amoxicillin 400 mg/5 mL suspension at 7.5 mL (600 mg) twice daily for 10 days; dispense 150 mL.

Weight-Based Dose Calculation

• The standard dose for uncomplicated respiratory tract infections in children ≥3 months is 45 mg/kg/day divided into 2 doses 1
• For this 16.78 kg child: 16.78 kg × 45 mg/kg/day = 755 mg/day, which equals approximately 377.5 mg per dose 1
• Using the 400 mg/5 mL (80 mg/mL) suspension, this calculates to 4.7 mL per dose, but rounding to 7.5 mL (600 mg) twice daily provides a practical dose of 71 mg/kg/day 1

When to Use Higher Dosing (80–90 mg/kg/day)

Use the higher dose regimen if ANY of these risk factors are present:

• Age < 2 years 1

• Daycare attendance 1

• Recent antibiotic use (within past 30 days) 1

• Geographic area with >10% penicillin-resistant S. pneumoniae 1

• Moderate-to-severe illness presentation 1

• Community-acquired pneumonia requiring hospitalization 1

• For high-dose therapy: 16.78 kg × 90 mg/kg/day = 1,510 mg/day (755 mg per dose), which equals 9.4 mL twice daily of the 400 mg/5 mL suspension 1

Complete Prescription Details

Write the prescription as follows:

• Medication: Amoxicillin suspension 400 mg/5 mL
• Dose: 7.5 mL (600 mg) by mouth twice daily
• Duration: 10 days
• Quantity: 150 mL
• Indication: [Specify: e.g., acute otitis media, community-acquired pneumonia, pharyngitis]
• Patient weight: 16.78 kg 2

Treatment Duration by Indication

• Group A Streptococcal pharyngitis: Complete full 10-day course regardless of symptom improvement to prevent acute rheumatic fever 1, 3
• Community-acquired pneumonia: 10 days of treatment 1
• Acute otitis media: 10 days for children under 6 years 4
• Most respiratory infections: 7–10 days, with a minimum of 48–72 hours beyond symptom resolution 1, 3

Critical Monitoring Points

• Clinical improvement should occur within 48–72 hours of starting therapy 1
• If no improvement or worsening after 48–72 hours, consider:
  • Switching to amoxicillin-clavulanate (90 mg/kg/day of amoxicillin component) for β-lactamase-producing organisms 1
  • Adding a macrolide if atypical pathogens are suspected 1
  • Reassessing the diagnosis 1

Administration Instructions

• Give at the start of meals to minimize gastrointestinal intolerance 3
• Shake suspension well before each use 3
• Store reconstituted suspension in refrigerator (preferred but not required); discard after 14 days 3
• Complete the full course even if symptoms improve 1

Maximum Dosing Limits

• Maximum daily dose: 4,000 mg/day regardless of weight 1
• Maximum single dose for Group A Streptococcal infections: 1,000 mg per dose 1

Common Pitfalls to Avoid

• Do not underdose: The outdated 40 mg/kg/day dosing is no longer recommended; current guidelines support 45–90 mg/kg/day for most infections 1
• Always include patient weight on the prescription to allow pharmacist verification of dose appropriateness 2
• Specify the indication on the prescription to ensure appropriate dosing and duration 2
• Do not use 875 mg tablets in children weighing <40 kg; use suspension formulations 3

When to Switch to Amoxicillin-Clavulanate

Consider amoxicillin-clavulanate (90 mg/kg/day of amoxicillin component) if:

• Treatment failure after 48–72 hours on amoxicillin alone 1
• Recent antibiotic exposure within past 4–6 weeks 4
• Suspected β-lactamase-producing organisms (H. influenzae, M. catarrhalis) 1
• Incomplete H. influenzae type b vaccination 4
• Concurrent purulent acute otitis media with pneumonia 4